Simply speaking Autosuggestion means suggesting oneself. Autosuggestion applies to all suggestion and self administered stimuli that reach one’s own mind through the five senses. No thought, whether it is negative or positive, can enter the subconscious mind without the aid of principle of Autosuggestion, with the exception of thoughts picked up from the ether.
Nature has so built us that we have complete control over the material which reaches our subconscious mind through our five senses, although this is not meant to be constructed as a statement that we always exercise this control. In great majority of cases, we do not exercise it, which explains why many people go through poverty in their life.
So basically all we have to do, is auto suggest our subconscious mind that we have to achieve what we desire and through hard work and practice, we can very well achieve the riches we want. Brain is a very dangerous thing, either it can help you to do wonders or it will help you to do worst. So you must control your mind, and it can be done with this principle of Autosuggestion.